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  #1  
Old 07-27-2003, 12:16 AM
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88 560SL ac center vent

Hi all

does any one know what would cause the center vent to stop working in the SL - I still get cold air out of the side vents but now it is stuck sending air to the defroster -- I did a search but can not see anything that matches -- I think I remember a vac control to the left of the ac dash control - I thought that that only opened and closed the center vent -- why does it come out of the defroster?

I just had the system checked -- they evac and recharged and fixed the pressure switch in the dryer for the aux fan as well as some inline fuse -- this is not related I know -- but I took it out today and all was great rode for about an hour including stop and go -- never even hit the 100 mark -- when I restart plenty of cold air just not from the center vent.

I have to say that I hate the ACC in this car - My dads SEL years ago was just as bad -- I wish it was manual.

Thanks any and all
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  #2  
Old 07-27-2003, 08:07 PM
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I tried to figure it out -- some one out in cyberspace must know the ac answer.

please -- its hot

thanks
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  #3  
Old 07-27-2003, 11:02 PM
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Join Date: Mar 2000
Location: Gainesville FL
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Can be nasty.

Ther center duct and the defroster duct are on the same vacuum one closes with vacuum (defrost) and one opens. I think the same vacuum might work a portion of recirc also. A leak in one can put all of them in the off position. Off is max recirc, defrost, closed center vent.

Just so happens that I took some pictures last month of one that took more than a vacuum leak. The center duct vac element is inside the heater/AC box and the attacment had broken and been really rigged from the outside.

I am going to paste three pictures in three different posts (as I don't know how to do it in one). The first one in this post will be an overview with the dash removed and the upper housing removed. The second will be the housing on the dash showing the cracked housing at cntr duct element. The third will be back together with a piece of plumbers strap pop-riveted and epoxied to reinforce.
Attached Thumbnails
88 560SL ac center vent-560sl-center-duct.jpg  
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33 years MB technician
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  #4  
Old 07-27-2003, 11:04 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
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You don't have vacuum in the AC system -- all the flaps are vac operated.

This can be because there is a line broken, or because you have a bad servo in the climate control.

Get under the hood and check the green plastic vac lines -- they run next to the brake booster. Make sure they are connected to the manifold and there are no breaks or bad rubber hose bits (this is the usual problem).

If it looks OK, you will then need to pull a vacuum on the climate control and see if it works -- if it works, you have a source problem (most likely a bad connector), if it won' hold vac you will have to track it down.

Peter
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  #5  
Old 07-27-2003, 11:06 PM
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this picture shows the defrost element and shows the broken attachment for the center duct element on the inside.
Attached Thumbnails
88 560SL ac center vent-560sl-center-duct2.jpg  
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Steve Brotherton
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33 years MB technician
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  #6  
Old 07-27-2003, 11:10 PM
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This picture shows the upper cover reattached and shows the reinforcement.

The main point to the pictures is for location reference, as I have never seen the case break like this before.
Attached Thumbnails
88 560SL ac center vent-560sl-center-duct3.jpg  
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Steve Brotherton
Continental Imports
Gainesville FL
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33 years MB technician
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  #7  
Old 07-31-2003, 03:37 AM
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Location: Phoenix, AZ
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I had the same problem in my car (86 560SEL)....... If you that you have good vacuum/ vacuum components, and the cold air comes out the defrost all or most of the time, I changed out the ACC PB panel. I was told that these were high failure items and it was my last resort before i took it to a shop. I ended up buying a rebuilt one for $155 and now she works like a freezer and blows cold through the proper vents.
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